US Patent 7459782 Stiffener for flip chip BGA package

Provided are semiconductor die flip chip packages with warpage control and fabrication methods for such packages. A package includes a heat spreader that is attached to a die and a stiffener, which are in turn attached to a package substrate. In general, the stiffener is made of a material that has a relatively low CTE value. For example, the stiffener material may have a CTE value less than 12 ppm/° C. The material may also have a relatively low mass density value of less than 8.9 g/cm3. Such a material may include natural graphite or some composite form of it. The result is a package with less bowing and so improved co-planarity (e.g., in compliance with industry specifications) with the surface to which it is ultimately bound; thereby, improving the reliability of the package. Moreover, a package that is relatively lighter and more robust than conventional semiconductor die flip chip packages can be realized.